In outside telephone plant, facilities must be provided for interconnecting feeder and distribution cables. Feeder cables extend from central offices to distribution areas where they are connected to distribution cables. The distribution cables are run to high density areas such as office buildings, for example, or to subdivisions where they are connected to service cables that extend to customers' premises.
A serving area interface is used to establish electrical connections between the feeder cables and the distribution cables. Typically, the interface is housed in a cabinet which is positioned in a location where it is safe from damage by vehicular traffic and flooding, where it is acceptable to property owners, and where it is not hazardous to employees and the public.
The connections are made through terminals which are mounted in rows and in columns in plastic terminal blocks that are supported in the cabinet. Feeder and distribution cables are brought into the cabinet and connected to the terminals. The terminals may be quick-connect type arrangements such as a bifurcated beam shown in U.S. Pat. No. 3,611,264 which issued on Oct. 5, 1971 in the names of B. C. Ellis et al. An earlier design terminal which is enjoying revived interest because of its excellent reliability is a binding post terminal.
In one prior art binding post arrangement, a terminal is made of rod material which is drilled and tapped at one end to form a barrel portion. A terminal screw, which comprises a threaded member having a head and two captive washers at one end, is turned into the barrel portion. From the other end of the terminal extends a wire wrapping portion. Conductors of a wiring harness are connected to selected wire wrapping portions after which the back side of each terminal block is encapsulated with a protective compound.
Conductors of the feeder and distribution cables are spliced to the conductors of the wiring harness. Field connections are made by crossconnecting jumpers between appropriate terminals that are connected to the conductors of the distribution cables and terminals that are connected to the conductors of the feeder cables. A field connection to a terminal is made by positioning a bared end of an insulated conductor between the two washers and wrapping the conductor about the terminal screw adjacent to its headed end. Then the screw is turned into the terminal to secure the conductor between the headed end and the terminal.
The manufacture of the terminal itself has been costly. Conventionally, it is necessary either to machine the entire part or to stamp a portion of it and weld on a separately machined threaded element. The machining has been accomplished by cold heading and tapping a blank having a barrel formed thereon. The wire-wrapping portion has been formed by coining and trimming one end portion of the blank.
Efforts have been made to produce internally threaded parts such as these terminals in other ways. For example, blanks have been engaged with a die having a threaded contour after which the blanks are formed into a cylindrical shape.
In U.S. Pat. No. 4,266,310, grooves are formed in a blank which is destined to become a terminal through opposed rectilinear motion between a punch and a die. The opposite edges of the grooved portions of the blank are brought together and the blank is given a cylindrical shape having an unjoined longitudinal seam. This, of course, requires precision forming of the blank in order to assure a match up of the grooves to form the internally threaded portion of the terminal. Inasmuch as the seam is not joined, axial forces could cause displacement of adjacent thread grooves and may prevent turning of the terminal screw into the barrel. On the other hand, to weld the seam would require that the thread grooves be aligned perfectly before the welding.
These efforts have not been altogether successful in producing a terminal having an accurately shaped thread. Consequently, traditional machining techniques have remained predominant in the terminal forming art.
Problems have also been encountered in the mounting of the terminals in the plastic blocks. In the past, the terminals have extended above the plastic terminal block. To prevent shorting between adjacent terminals during interconnection, the terminal barrels have been coated with an epoxy insulating material. Needless to say, this increases the cost of this terminal block arrangement.
Another problem that concerns the mounting of the terminals in the plastic block has surfaced. Barbs formed on and protruding from the terminal are wedged into the plastic as the terminal is inserted into an opening in the block. Stresses which are induced during the insertion of such a terminal become residual. When connections are made to the terminal block, additional stresses are imparted to the plastic. In some instances, the combination of stresses has been sufficient to cause a cracking of the plastic block.
What is needed and what is not shown in the prior art are methods of making a terminal which has an internally threaded portion and which is relatively low in cost. The terminal must be one which has a quality threaded portion to minimize the time required of installers to turn a terminal screw into the terminal barrel. Also, the terminals and their mounting block arrangement desirably should be such that electrical shorting between adjacent terminals and residual stressing of the plastic block are avoided.